This invention relates to a bag with free swiveling caster wheels provided in the four corner regions of the bottom of the bag, and in particular to a bag that can move in any direction in a horizontal plane while standing independently on freely rotating caster wheels.
The present inventor has developed a bag which can stand independently and is free to move in any direction. This bag has free swiveling caster wheels mounted on the bottom surface of the main bag. Free swiveling caster wheels are provided at the four corners of the bottom surface of the main bag to allow it to stand on its own in a vertical position. A handle for moving the bag extends upwards and is connected to the main bag. A bag of this configuration can move freely in any direction while in a vertical standing position. A bag, which is moveable in this position, can be readily moved in crowded areas. In addition, it has the feature that it can be moved while being used as a supporting cane. Further, since the four caster wheels are free to move in any direction, the bag can freely move in any direction while standing in a vertical position. A vertically standing bag does not apply any of its weight to the handle. Therefore, even an extremely heavy bag can be easily moved simply by pushing.
In a bag with this structure, standing can become unstable when the lateral width of the bag is narrowed. Since free swiveling caster wheel direction naturally changes according to the direction of bag movement, instability can result from inconsistency in the movement direction. For example, when a bag is moved sideways in the direction shown by arrow A in FIG. 1, the bag can fall in the direction of movement as shown by arrow B. This is because caster wheels 41 on both sides of the bag face in the same direction, and the center of support for caster wheels 41 on both sides shifts from the center of the main bag 43. Further, if the main bag 43 is moved left and right as shown in FIG. 2, caster wheels 41 on both sides of the bag can face opposite directions, and the distance between wheels 46 can become narrower. In this case, the main bag can more easily fall to either side.
This drawback can be eliminated by making the main bag wider. However, if the main bag is made wider, it will become large, heavy, and inconvenient to use. It is necessary to design main bag width at sizes that are convenient for user application. If main bag width is increased to make it less likely to fall over, drawbacks, such as limited applications, arise.
Bag stability can also be improved by reducing the eccentricity of the free swiveling caster wheels. As shown in FIG. 1, an eccentricity distance (S) is established between the rotation axis 47 of the wheel 46 and the swivel shaft 49 of a free swiveling caster 41. The eccentricity distance (S) is the distance between the swivel axis m, which is the center of rotation of the swivel shaft 49, and a point where a horizontal plane is tangent to the wheel 46. It is necessary to provide a free swiveling caster wheel with a certain eccentricity distance (S). This is because the direction of a free swiveling caster wheel 41 should change automatically with movement of the main bag 43. As shown in FIG. 1, when the bag is moved in the direction of arrow A, each free swiveling caster wheel 41 swivels to position the point where the wheel 46 touches the ground, behind the swivel axis m, which is the center of rotation of the swivel shaft 49. By swiveling in this direction, the free swiveling caster wheels 41 allow the bag to move smoothly in any direction. If the eccentricity distance (S) is reduced, the swiveling ability of the caster will decrease and the caster will become unstable. Therefore, a certain eccentricity distance (S) is required for a free swiveling caster wheel. Although it is not illustrated, an example of a prior art free swiveling caster wheel had a yoke, which rotated in a horizontal plane, and a mount, which attached to the bottom of the main bag. This prior art configuration joined the yoke to the mount via steel balls and guide grooves to allow the yoke to swivel. In this free swiveling caster wheel structure, friction between the steel balls and rotation guide grooves prevented yoke rotation with light force, and it was necessary to increase the eccentricity distance (S) for swiveling. Further, because some play was required between the steel balls and rotation guide grooves, this caster wheel configuration had the drawback that loud noise would result when the bag was moved at night on a poorly paved walkway.
The eccentricity distance (S) of a free swiveling caster wheel can be shortened if the yoke can swivel with extremely small force, that is, if the yoke can smoothly rotate around the swivel shaft. A free swiveling caster wheel provided with a radial bearing has been developed to reduce rotational torque on the swivel shaft (refer to Japanese Patent Application Disclosure 2002-347408; and Japanese Patent Application Disclosure 2003-191705).
The free swiveling caster wheel cited in the disclosure of JP 2002-347408 has a radial bearing connected to the swivel shaft. The swivel shaft inserts into the inner ring of the radial bearing and the yoke is connected with the outer ring to allow the yoke, with wheel attached, to smoothly swivel via the bearing. In addition to allowing smooth swiveling, this caster wheel configuration has the characteristic that almost no noise is made even when moving on an uneven surface because there is almost no play in the ball bearings. However, if an impact load acts on the bag, bending stress will be applied to the swivel shaft of this free swiveling caster wheel. This is because an eccentricity distance (S) is established between the swivel shaft and the rotation axis of the wheel. This bending stress can be the cause of damage to the radial bearing. Since the radial bearing is designed to support forces perpendicular to its rotation axis, it does not have sufficient strength with respect to bending stresses. Consequently, if a strong impact load acts on the bag and strong bending stress is applied to a caster wheel, damage to rolling surfaces of the steel ball bearings, inner ring, and outer ring can occur in the radial bearing, and the caster will not rotate smoothly or can generate noise when rotating.
The free swiveling caster wheel cited in the disclosure of JP 2003-191705 has two radial bearings stacked top and bottom, and the yoke is sandwiched between the two radial bearings. In this caster wheel configuration, bending stresses are supported by two radial bearings. Consequently, this configuration is stronger with respect to bending stresses than that of JP 2002-347408. However, when two radial bearings are used, the drawback arises that manufacturing cost increases significantly. Further, since strong bending impact forces are being supported by radial bearings designed to support forces perpendicular to their rotation axes, it is difficult to insure sufficient strength in all cases, even when two bearings are stacked together. Bending impact forces cannot be eliminated because the bag can travel on surfaces with bumps and ruts, and because it can be dropped and receive a strong impact. Consequently, this free swiveling caster wheel has the drawback that even though radial bearings are used on the swivel shaft, swiveling becomes rough after a certain period of use.
The present invention was developed to further resolve the drawbacks described above. Thus it is a primary object of the present invention to provide a bag with caster wheels wherein even if strong impact forces act on the main bag, free swiveling caster damage is remarkably rare, casters can swivel extremely smoothly, and the bag can freely move in any direction without applying a large amount of force.
Another important object of the present invention is to provide a bag with caster wheels wherein the eccentricity distance of the free swiveling caster wheels is reduced to allow the bag to stand on its own, in a stable fashion even when main bag width is reduced.
The above and further objects and features of the invention will be more fully apparent from the following detailed description with the accompanying drawings.